Selective elimination of the C-terminal amino group of peptide amides is generally difficult to achieve by a chemical reaction because the peptide linkage is also subject to hydrolytic attack. Amidases which cleave amide group are known but these enzymes do not catalyze the cleavage of peptide amides and therefore, because of their .alpha.-amino acid amidase activity (DE-OS 36 29 242), can only be employed in the preparation of L-amino acids from .alpha.-unprotected amides of D,L-amino acids.
In addition to the foregoing amidases, peptidases which catalyze the hydrolytic cleavage of peptide linkages have merely a certain secondary activity for eliminating the C-terminal amino protective group are known. Carboxypeptidase Y is illustrative of these peptidases, especially in a chemically modified form (see K. Breddam, Carlsberg Res. Commun. 49 (1984) 535-54).
Accordingly, the enzymatic elimination of the free amino group of peptide amides without the simultaneous cleavage of peptide linkages has been considered infeasible heretofore.